Semiconductor devices such as logic and memory devices are typically fabricated by a sequence of processing steps applied to a substrate or wafer. The various features and multiple structural levels of the semiconductor devices are formed by these processing steps. For example, lithography among others is one semiconductor fabrication process that involves generating a pattern on a semiconductor wafer. Additional examples of semiconductor fabrication processes include, but are not limited to, chemical-mechanical polishing, etch, deposition, and ion implantation. Multiple semiconductor devices may be fabricated on a single semiconductor wafer and then separated into individual semiconductor devices.
Inspection processes are used at various steps during a semiconductor manufacturing process to detect defects on wafers to promote higher yield. As design rules and process windows continue to shrink in size, inspection systems are required to capture a wider range of physical defects on wafer surfaces while maintaining high throughput.
One such inspection system is a surface inspection system that illuminates and inspects an unpatterned wafer surface for undesired particles. As semiconductor design rules continue to evolve, the minimum particle size that must be detected by a surface inspection system continues to shrink in size.
To detect smaller particles, laser scattering based inspection tools must increase the laser power density of the illumination light. However, in some examples, high illumination power density causes large size particles to explode due to high power laser heating. This creates hundreds of smaller particles on the wafer and compounds the contamination problem. In other examples, higher illumination power density damages films deposited on the wafer or the wafer itself.
Typically, overall incident beam power is reduced by dumping a portion of the illumination light generated by the illumination source to avoid reaching the thermal damage threshold. In some examples, a significant amount of the beam power generated by the illumination source is dumped to avoid damaging the wafer. In typical bare wafer applications that are shot noise limited, the loss of overall beam power results in a loss of defect detection sensitivity.
Improvements to scanning surface inspection systems are desired to detect defects in the inspection path of an illumination spot on a wafer surface with greater sensitivity while avoiding large particle fragmentation and thermal damage to the wafer surface.